He said the current DVLA system was "not fit for practice'', adding that it was possible for a person applying for a licence "to not disclose very important things''.

He added: "Unless this goes through the GP in some shape or form there's a very, very real risk of a medical condition not being disclosed.''

Asked about the cost implications of any such change, he added: "I wouldn't want to put a cost on public safety.

"Whatever it takes we have to make sure that persons driving our buses and lorries are entitled to do so and safe to do so.''

Earlier, the inquiry heard that Mr Clarke told Prof Rankin at their February meeting that he had not lost consciousness during the 2010 incident.

During cross-examination, Dorothy Bain QC, representing the family of victim Jacqueline Morton, put it to the witness that Mr Clarke had given him a "completely different'' account of the 2010 incident to that given to other doctors.

"He told me that he had not actually lost consciousness,'' the professor told the court.

Prof Rankin agreed that he appeared to have been given a different account to that given to other doctors that Mr Clarke had in fact "blacked out''.

Mr Clarke has been suspended from work by Glasgow City Council ''on a precautionary basis'' ahead of a full investigation.

The Crown Office said in February that no criminal charges would be brought against Mr Clarke in relation to the crash but relatives of Ms Morton have called for him to be prosecuted.

Ms Morton, 51, and Ms Tait, 29, both from Glasgow, and Gillian Ewing, 52, from Edinburgh, were killed as the lorry travelled out of control along Queen Street and towards George Square before crashing in to the side of the Millennium Hotel.

Erin McQuade, 18, and her grandparents Jack Sweeney, 68, and Lorraine Sweeney, 69, from Dumbarton, West Dunbartonshire, also died from multiple injuries after being hit by the truck.